Over two-thirds of the British population is considered to be overweight or obese, according to the National Health Society. A 2013 report found that the UK has the highest level of obesity in Western Europe.

The chart below, created by the RSPH, shows the duration of exercise required to burn off calories in a number of popular foods.

For example, if you eat one-quarter of a large pizza containing 449 calories, you would need to walk for one hour and 23 minutes or run for 43 minutes to burn it off. For a bar of milk chocolate with 229 calories, you would need to go on a 42-minute walk or a 22-minute run. Royal Society of Public Health

Here's how these labels might look on a food product, such as a chocolate bar. The label shows how long you would have to run, cycle, or swim.

Royal Society of Public Health

"We think a clearer way of making people more mindful of the calories they are consuming is for a food or drink product to also show on the front of the packet a small icon which would visually display just how much activity you would need to do to burn off the calories it contains," Shirley Cramer, chief executive of the RSPH, wrote in a BBC article.

But the new labels are far from appearing on supermarket items.

"We believe further research is needed into whether activity equivalent calorie information could be an effective way of encouraging consumers to achieve a healthier lifestyle," Tim Rycroft, corporate affairs director of the Food and Drink Federation — the representing body of the UK's food- and drink-manufacturing industry — said in a recent statement on its website.

He added: "EU rules which dictate what companies can and cannot put on their food labels would need to be considered in any proposals to add to on-pack information."

One food company that's already using a similar label is the snack manufacturer Taking the Pea, which has included an icon of an exercising pea on the back of its snack packets with the amount of exercise required to expend the calories inside.

The RSPH is not currently aware of any other food companies using activity equivalent labelling on their products, according to Ed Morrow, the organisation's PR and Campaigns Manager.